(1) Field of the Invention
The invention relates generally to the field of the anticorrosion protection of pipelines.
The term “pipeline” is understood to mean a conduit for the long-distance transportation of fluids, such as water, petroleum products, gas or drainage products.
More specifically, the invention relates, according to a first of its aspects, to a process for application of a monolayer or multilayer anticorrosion coating to a metal substrate forming part of a pipe or of a fitting of a pipeline intended to be buried or immersed for the transportation of fluids, such as water, petroleum products, gas or drainage products.
(2) Prior Art
The anticorrosion protection of a pipeline, in other words of a buried or immersed conduit used in particular for the transportation of water, oil or gas, has been based on the same principle for decades: an adhesive organic coating, which is a passive barrier to water and to oxygen, coupled to electrochemical active protection which consists in bringing the material constituting the pipeline to a potential such that any oxidation of the iron forming part of the composition of these materials is inhibited. It has always been carried out either by the method of a sacrificial anode or by impressed current. Cathodic protection is involved.
The various systems of organic coatings used in the field of anticorrosion protection of pipelines or conduits include systems based on epoxy powder paints of high reactivity used as monolayer coating or as primer of a complex “multilayer” system, for example a three-layer system, as it is composed of this primer, of an adhesive based on modified polyolefin and of a final polyolefin-based layer.
The organic coatings intended for the anticorrosion protection of pipelines are subject to operating stresses which combine temperature and humidity. This is because the pipelines can be buried in a more or less wet soil or placed on the seabed. Moreover, the fluid may be heated in order to lower its viscosity so as to minimize the head losses which occur during transportation within the pipeline network, the length of which can represent from several hundred to several thousand kilometers.
The operating temperature can vary from 20 to 150 degrees Celsius (° C.). The combination of temperature and humidity results in an acceleration in the penetration of water into the coating material. This phenomenon is reflected by a loss in adhesion of the coating with regard to the metal support constituting the pipeline.
The loss in adhesion is harmful to the continuity of the anticorrosion protection.
The pipeline components are conventionally subjected to a surface preparation which can consist in mechanically blasting the substrate.
Chemical treatments of the metal surfaces can also be employed after this surface preparation in order to improve the adhesion in a wet environment of the organic coatings. These chemical treatments are conventionally based on chromates or on phosphates.
There are several disadvantages to the application of solutions based on chromates or on phosphates. The application involves rinsing operations, which complicate the application process and result in the formation of additional waste. It involves, after drying, an operation for the thermal conversion of the chromates or phosphates, which renders the process expensive. It involves the use of toxic products, in the case of the chromates.